Summary - Project 1 (PD: Michel Nussenzweig) The re-emergence of Zika virus (ZIKV) poses serious threats to human health because of the dire consequences on the fetus when infection occurs during pregnancy. Based on the distribution of its mosquito vector, ZIKV threatens up to 40% of the world's population. There are no treatments or prophylaxis against ZIKV, which makes the design of vaccines urgent and highly desirable. Numerous vaccine candidates are already being pursued that use as an approach the whole virus or large portions of the virus Envelope protein (E). Although this approach seems efficacious and promising in pre-clinical models, serious concerns exist with regard to safety due to the phenomenon of Antibody Dependent Enhancement (ADE) and cross-reactivity with dengue virus (DENV). A ZIKV vaccine of such design could elicit antibodies that cross-react with but do not neutralize DENV, possibly making a vaccinated individual more susceptible to severe dengue disease through ADE. In contrast, a vaccine designed to focus exclusively on neutralizing epitopes is more likely to be safe. The Nussenzweig lab has discovered human antibodies that potently neutralize ZIKV by recognizing non- overlapping epitopes on the Zika Envelope Domain III (ZEDIII), and in collaboration with the Bjorkman lab has started to structurally define their cognate epitopes on the viral surface. The long-term goal of this proposal is to develop and evaluate immunogens that preferentially elicit antibodies that target ZIKV neutralizing epitopes and do not enhance dengue infection. To accomplish this, Dr. Nussenzweig will work with Dr. Bjorkman to characterize novel neutralizing epitopes on the viral surface of ZIKV. This information will be harnessed to design novel immunogens that preferentially drive the generation of neutralizing antibodies to these epitopes. For example, candidate immunogens will be designed and evaluated to elicit human VH3-23/VK1-5 antibodies that are recurrent and potent neutralizers of ZIKV in humans. The Nussenzweig lab plans to 1) discover more antibodies that neutralize ZIKV in order to generate a panel of additional non-overlapping neutralizing viral epitopes; 2) use this information to help the Bjorkman lab design novel immunogens that preferentially elicit protective antibodies to such epitopes; 3) evaluate these immunogens in wild type mice; 4) extend the evaluation of the most promising immunogens to genetically humanized mice; 5) assess vaccine efficacy using ZIKV-susceptible mouse models; 6) evaluate vaccine cross- protection by challenging the immunized mice with DENV; and 7) evaluate ADE by challenging vaccinated mice with sub-lethal doses of DENV. Overall, the proposed experiments bear a significant translational potential, and are expected to result in candidate vaccines for subsequent evaluation in non-human primate models and vaccine clinical trials.